human physiology

• Normal blood sugar level


  • 70 to 100 milligrams per deciliter (100 ml) after fasting for eight hours
  • Rises to no more than 140 milligrams per deciliter within two hours of eating
• Dangerously high blood sugar level

  Above 180 milligrams per deciliter
• Dangerously low blood sugar level

  Below 50 milligrams per deciliter (hypoglycemic)
• Consistently high blood sugar levels

  Glucose acts as a poison to certain organs, such as the pancreas which becomes permanently damaged
• High blood sugar levels

  Can lead to cardiovascular disease and blindness
• Homeostasis


  A mechanism that maintains a stable internal environment despite the changes present in the external environment
• Claude Bernard (1813 –1878) was a French Physiologist who defined the term milieu interieur (internal environment)
• Milieu intérieur is the key process with which Bernard is associated. He wrote, "The constancy of the internal environment is the condition for a free and independent life"
• Homeostasis


  (homeo – similar; stasis standing still), yielding the idea of "staying the same"
• Homeostasis


  The condition of the internal environment being maintained within relatively narrow limits
• Walter Cannon (1871-1945) came up with the term HOMEOSTASIS in 1926 and defined it as the physiological systems functioning to maintain or regulate the condition of the internal environment within relatively narrow limits
• Salmons provide an excellent example of chloride ion regulation, maintaining a nearly constant concentration of Cl- ions in their blood regardless of how low or high the outside concentration is
• Water in cells


  In thermodynamic equilibrium across the plasma membrane, with osmotic concentrations of cytoplasmic and extracellular fluids equal under steady-state conditions
• Changes in intracellular or extracellular solute concentrations generate a transmembrane osmotic gradient, causing immediate flow of water into or out of the cell until osmotic equilibrium is restored
• Most cells of an animal are exposed to the internal environment, not the external environment
• Each functional structure in the body provides its share in the maintenance of homeostatic conditions in the extracellular fluid, which is called the internal environment
• Homeostatic mechanisms of the major functional systems

  • Lungs provide oxygen
  • Gastrointestinal system provides nutrients
  • Kidneys regulate concentrations of hydrogen, sodium, potassium, phosphate, and other ions, and excrete urea
  • Liver and pancreas regulate the concentration of glucose
• Concepts of homeostasis


  • Physico-chemical properties of the body fluids
  • Intracellular and extracellular media
  • Temperature
  • Blood pressure
  • Osmolarity
  • Energy supply
• Control systems of the body

  Receptor - senses changes, control centre - processes information, effector - acts to restore normal state
• Regulation of arterial blood pressure involves the baroreceptor system, with nerve receptors in the walls of the carotid arteries and aortic arch that are stimulated by stretch of the arterial wall
• Set point


  The value of the regulated variable that the system wants to maintain
• Changes in physiology can be responses to changes in the external environment or internally programmed to occur, such as circadian rhythms in melatonin secretion
• Disruption of homeostasis


  Leads to disease or cell malfunction, caused by either deficiency (cells not getting all they need) or toxicity (cells being poisoned by things they do not need)
• Regulation of the Circulation

  The blood flow must be regulated to ensure an adequate blood supply, even under changing environmental conditions and stress
• The blood flow to each tissue usually is regulated at the minimal level that will supply the tissue's requirements— no more, no less
• Optimal regulation of the circulation

  • Optimal regulation of cardiac activity and blood pressure
  • Adequate perfusion of all organ systems
  • Shunting of blood to active organ systems at the expense of the resting organs to keep from overtaxing the heart
• Regulation of blood flow to the organs


  Mainly achieved by changing the diameter of blood vessels
• Vascular smooth musculature


  Has an intermediary muscle tone at rest (resting tone)
• Regulation of blood flow to the organs

  1. Local stimuli

  2. Hormonal signals

  3. Neuronal signals
• Active hyperemia


  When the tissues use more oxygen, the blood flow increases
• Active hyperemia


  • Increase in blood flow that accompanies muscle contraction (exercise or functional hyperemia in skeletal muscle)
  • Increase in gastrointestinal blood flow during digestion
  • Increase in coronary blood flow when heart rate is increased
  • Increase in cerebral blood flow associated with increased neuronal activity in the brain
• There is a resting flow associated with the basal oxygen consumption of the tissue. As the oxygen consumption increases, there is generally a near-linear increase in blood flow until the vessels begin to achieve a maximally dilated state
• Reactive hyperemia


  When the blood supply to a tissue is blocked for a short while and then is unblocked, blood flow through the tissue increases immediately to 4 to 7 times normal
• The skeletal muscle can increase local muscle blood flow as much as 20-fold during intense exercise
• Acute Local Blood Flow Regulation When Oxygen Availability Changes

  Whenever the availability of oxygen to the tissues decreases, the blood flow through the tissues increases markedly
• Acute Local Blood Flow Regulation When Oxygen Availability Changes

  • At high altitude
  • In pneumonia
  • In carbon monoxide poisoning
  • In cyanide poisoning
• Autoregulation


  Autoregulatory mechanisms help to maintain a constant blood flow to certain organs when the blood pressure changes
• Autoregulation also functions to adjust the blood flow according to changes in metabolic activity of an organ; the amount of blood flow to the organ (e.g., cardiac and skeletal muscle) can thereby increase many times higher than the resting level
• Local metabolic (chemical) effects

  An increase in local concentrations of metabolic products such as CO2, H+, ADP, AMP, adenosine, and K+ in the interstitium has a vasodilatory effect, especially in precapillary arterioles
• The resulting rise in blood flow not only improves the supply of substrates and O2, but also accelerates the efflux of these metabolic products from the tissue